Fuel cell energy supply system and control method thereof

Abstract

The invention discloses a fuel cell energy supply system and a control method thereof. The device comprises an energy management device, a fuel cell, a storage battery, a one-way DCDC converter, a two-way DCDC converter, a bus bar and onboard loads connected with the bus bar, wherein the fuel cell, the storage battery, the one-way DCDC converter, the two-way DCDC converter and the bus bar are connected with the energy management device. The fuel cell serves as a main power source, is connected to the bus bar through the one-way DCDC converter and is used for providing basic electric energy for all loads, and voltage stabilization and power conversion are conducted through the one-way DCDC converter. The storage battery serves as an auxiliary power supply, is connected to the bus bar through a bidirectional DCDC and is used for performing power compensation on each load; the energy management device is used for collecting airplane demand power in real time through the bus bar and distributing optimal output power for the fuel cell and the storage battery in the fuel cell energy supply system according to the fuel cell state and the charge state of the storage battery which are collected in real time. According to the technical scheme, the problem that the output power of the fuel cell is not optimal due to the fact that the existing energy management control mode of the fuel cell energy supply system only considers the minimum equivalent hydrogen consumption of the fuel cell or carries out power adjustment according to the charge state of the storage battery is solved.

Description

Technical Field

[0001] The present invention relates to, but is not limited to, the technical field of fuel cells, and in particular to a fuel cell energy supply system and a control method thereof. Background Art

[0002] With the development of the times, the global aviation industry has gradually begun to move towards low-carbon, environmentally friendly all-electric propulsion. Fuel cell propulsion systems have attracted widespread attention from academia and industry due to their advantages such as zero pollution, low noise, high efficiency, and high energy density, and have become one of the potential development directions of green and low-carbon aviation.

[0003] The energy management control methods of existing fuel cell energy supply systems usually include power following control strategy, equivalent hydrogen consumption minimum strategy, fuzzy control strategy and state machine strategy. The power following control strategy uses the overall power demand of the aircraft system and the charge state of the battery as input, and adjusts the power distribution of the fuel cell and the battery according to the load demand power and the battery state of charge (SOC) reference value. The equivalent hydrogen consumption minimum strategy is to minimize the hydrogen consumption, and the power distribution is carried out with the minimum hydrogen consumption as the objective function. The fuzzy control strategy also takes the system demand power and the battery SOC as input, and completes the power distribution through the designed fuzzy control rules. The state machine strategy divides the working state of the hybrid system formed by the fuel cell and the battery into a limited number of states by dividing the battery SOC area and the load demand power area, and then determines the fuel cell power reference value in each state.

[0004] Existing fuel cell energy supply systems are mainly used in the field of drones and small aircraft. Most of their energy management and control methods only consider the minimum equivalent hydrogen consumption of the fuel cell or adjust the power according to the battery charge state, but do not consider the working state of the fuel cell itself. Summary of the invention

[0005] Purpose of the present invention: In order to solve the above-mentioned technical problems, an embodiment of the present invention provides a fuel cell energy supply system and a control method thereof, so as to solve the problem that the existing energy management control method of the fuel cell energy supply system only considers the minimum equivalent hydrogen consumption of the fuel cell or adjusts the power according to the battery charge state, resulting in the problem that the output power of the fuel cell is not optimal.

[0006] Technical solution of the present invention: In a first aspect, an embodiment of the present invention provides a fuel cell energy supply system, comprising: an energy management device, a fuel cell, a battery, a unidirectional DCDC converter, a bidirectional DCDC converter, a bus bar respectively connected to the energy management device, and various onboard loads connected to the bus bar;

[0007] The fuel cell is used as the main power source and is connected to the bus bar through a unidirectional DCDC converter to provide basic power for each load, and the unidirectional DCDC converter performs voltage stabilization and power conversion;

[0008] The battery is used as an auxiliary power source and is connected to the busbar via a bidirectional DCDC to provide power compensation for each load;

[0009] The energy management device is used to collect the aircraft power demand in real time through the bus bar, and allocate the optimal output power to the fuel cell and battery in the fuel cell power supply system through the real-time collected fuel cell state and battery charge state.

[0010] Optionally, in the fuel cell energy supply system as described above,

[0011] The energy management device is configured with two PI control algorithm modules, and the two PI control algorithm modules correspondingly control the unidirectional DCDC converter and the bidirectional DCDC converter.

[0012] Optionally, in the fuel cell energy supply system as described above,

[0013] The input of the PI control algorithm module corresponding to the bidirectional DCDC converter is the voltage collected through the bus bar and the real-time current of the battery. The output of the bidirectional DCDC converter is controlled according to the allocated power to achieve the output voltage stability and automatic adjustment of the output current of the bidirectional DCDC converter;

[0014] The input of the PI control algorithm module corresponding to the unidirectional DCDC converter is the voltage collected through the bus bar and the real-time current of the fuel cell. The output of the unidirectional DCDC converter is controlled according to the allocated power to achieve the output voltage stability and automatic adjustment of the output current of the unidirectional DCDC converter.

[0015] In a second aspect, an embodiment of the present invention further provides a control method for a fuel cell energy supply system, wherein the control method is a control method for the output power of a fuel cell and a battery in a fuel cell energy supply system as described in any one of the above items, comprising:

[0016] Step 1: During the flight, the aircraft can monitor the bus voltage changes in real time to obtain the aircraft power demand P. req ;

[0017] Step 2: Use the model predictive control algorithm to achieve the optimal control effect at every moment as the control goal, and calculate the optimal power P of the fuel cell at the current moment. bestfc ;

[0018] Step 3: Real-time monitoring of the actual battery output voltage Vbat 、Current I bat And the state of charge SOC; during the real-time monitoring process, the battery charge and discharge are controlled to ensure that the battery SOC remains within the normal working range;

[0019] Step 4: Based on the real-time monitored aircraft power demand, the calculated optimal power of the fuel cell at the current moment, and the battery charge state, power is allocated through an energy management strategy to allocate optimal power to the fuel cell power supply system;

[0020] Step 5: According to the optimal power allocated to the fuel cell power supply system, the unidirectional DCDC converter and the bidirectional DCDC converter are controlled to adjust the output power of the fuel cell and the battery respectively.

[0021] Optionally, in the control method of the fuel cell energy supply system as described above, the step 2 of calculating the optimal power of the fuel cell at the current moment includes:

[0022] The current state of the fuel cell is monitored, and the model predictive control algorithm is used. The current low calorific value and hydrogen pressure of the fuel cell are used as the model input. Based on the historical data of the fuel cell and the future input predicted by the model, the optimal control effect is achieved at each moment as the control goal, and the optimal power P of the fuel cell at the current moment is obtained. bestfc .

[0023] Optionally, in the control method of the fuel cell energy supply system as described above, the step 2 of calculating the optimal power of the fuel cell at the current moment includes:

[0024] Step 21, set the objective function of the model predictive control algorithm to: f = minm H2 (t);

[0025] Step 22, according to the change of hydrogen pressure, the hydrogen consumption rate is obtained as follows:

[0026]

[0027] Wherein, p is the hydrogen pressure, n is the number of cells in the stack, M is the molar mass of hydrogen, V is the water volume of the hydrogen storage bottle and the volume of the pipeline, R is the gas constant of the hydrogen storage tank, T is the tank temperature, and Z is the hydrogen compression factor under the conditions of p and T;

[0028] Step 23, using the lower calorific value of hydrogen and the hydrogen consumption rate in actual measurement to obtain the optimal output power of the fuel cell at the current moment:

[0029] P bestfc =η fc L HV m H2 ;

[0030] Among them, L HV is the lower calorific value of hydrogen; η FC for the efficiency of the fuel cell;

[0031] Based on the power constraints of the fuel cell, the optimal power P of the fuel cell at the current moment is calculated. bestfc The power constraint of the fuel cell is as follows:

[0032] P fc_min ≤P fc (k)≤P fc_max ;

[0033] Among them, P fc_min is the minimum output power of the fuel cell, P fc_max is the maximum power that the fuel cell can output, P fc is the fuel cell power at the current moment.

[0034] Optionally, in the control method of the fuel cell energy supply system as described above, the energy management strategy in step 4 includes:

[0035] Strategy 1: When the fuel cell output power is insufficient to bear the aircraft's required power, that is, P fc <P req When the battery is discharged to the lower limit of the charge state, the discharge stops and the aircraft requires power P req Provided by fuel cells;

[0036] Strategy 2: When the fuel cell output power can meet the aircraft's required power, that is, P fc ≥P req When the SOC of the battery is reached, the fuel cell stops charging the battery through the bus.

[0037] Optionally, in the control method of the fuel cell energy supply system as described above,

[0038] The strategy 1 includes:

[0039] When the optimal power of the fuel cell at the current moment and the maximum discharge power of the battery cannot meet the aircraft's required power at the current moment, that is, P req -P bestfc >P dischgmax When the power distribution of the fuel cell and the battery is: the fuel cell and the battery both output at the maximum power, that is, P fc =P fcmax , P bat =Pdischgmax ;

[0040] When the fuel cell has the optimal output power P at the current moment bestfc The maximum discharge power of the battery can meet the aircraft's current power demand, that is, P req -P bestfc ≤P dischgmax When the power distribution of the fuel cell and the battery is: the fuel cell outputs the optimal power at the current moment, and the battery bears the remaining power required by the aircraft, that is, P fc =P bestfc , P bat =P req -P bestfc ;

[0041] Among them, the maximum discharge power of the battery is:

[0042]

[0043] Among them, v oc is the open circuit voltage of the battery, r dis is the internal resistance of the battery discharge, v o is the starting voltage of the battery.

[0044] Optionally, in the control method of the fuel cell energy supply system as described above, the strategy 2 includes:

[0045] If the battery SOC is greater than the target value, the battery does not need to be charged; the fuel cell only supplies power to the onboard load, and its output power is the load demand power, that is, P fc =P req ;

[0046] If the battery SOC is less than the target value, there are two cases: Case 1, when the optimal output power of the fuel cell at the current moment is greater than or equal to the sum of the aircraft's required power and the battery's maximum charging power, that is, P bestfc ≥P req +P chgmax , the power distribution of fuel cell and battery is: the output power of fuel cell is the sum of the aircraft power requirement and the battery power requirement, and the battery charging power is its maximum charging power, that is, P fc =P req +P bat , P bat =P chgmax ; Case 2: When the optimal output power of the fuel cell at the current moment is less than the sum of the aircraft's required power and the battery's maximum charging power, that is, P bestfc <P req +P chgmaxWhen the fuel cell and battery power are distributed, the fuel cell output power is the optimal output power at the current moment, and the battery charging power is the remaining power after the fuel cell supplies power to the onboard load, that is, P fc =P bestfc , P bat =P bestfc -P req ;

[0047] Among them, the maximum charging power of the battery is:

[0048]

[0049] Among them, r chg is the internal resistance of battery charging, v batmax The maximum allowable voltage of the battery.

[0050] Beneficial effects of the present invention: A fuel cell energy supply system and a control method thereof provided in an embodiment of the present invention, the fuel cell energy supply system comprises: an energy management device, a fuel cell, a battery, a unidirectional DCDC converter, a bidirectional DCDC converter, a bus bar connected to the energy management device respectively, and various loads on board connected to the bus bar; wherein, the fuel cell is used as the main power source, connected to the bus bar through a unidirectional DCDC converter, and provides basic power for the electrical equipment, and the unidirectional DCDC converter performs voltage stabilization and power conversion; the battery is used as an auxiliary power source and because it needs to be charged and discharged, the battery is connected to the bus bar through a bidirectional DCDC converter to perform power compensation for the electrical equipment. The fuel cell energy supply system provided in an embodiment of the present invention must not only meet the bus voltage stability on the bus bar, but also meet the power requirements when the load changes. Under different flight conditions, the energy management device controls the fuel cell and the battery to jointly power the electrical equipment on board.

[0051] In order to adjust the output power of the fuel cell and the battery as quickly as possible, the technical solution provided by the embodiment of the present invention adopts a PI control algorithm to control the DCDC converter in the energy management device. On the one hand, the bidirectional DCDC converter at the rear end of the battery adopts a double closed-loop control (the voltage loop is the outer loop and the current loop is the inner loop), and its corresponding PI control algorithm module controls the output of the bidirectional DCDC converter according to the voltage collected through the bus bar and the real-time current of the battery, so as to achieve the output voltage stability and automatic adjustment of the output current of the bidirectional DCDC converter; in addition, the steady-state characteristics and transient characteristics of the bidirectional DCDC can be improved through current feedback. On the other hand, the unidirectional DCDC at the rear end of the fuel cell also adopts a single closed-loop control, and the control loop is the fuel cell current loop. The unidirectional DCDC is controlled by the fuel cell power allocated by the energy management device and the actual output current of the fuel cell, so as to adjust the output power of the fuel cell. Since the output characteristics of the fuel cell are soft, the "oxygen starvation" phenomenon will occur when the load demand suddenly changes, and the bus voltage is in a stable state, so the fuel cell can be protected by controlling the output current value and current change rate of the fuel cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] The accompanying drawings are used to provide a further understanding of the technical solution of the present invention and constitute a part of the specification. Together with the embodiments of the present application, they are used to explain the technical solution of the present invention and do not constitute a limitation on the technical solution of the present invention.

[0053] Figure 1 A schematic diagram of the system structure of a fuel cell energy supply system provided by an embodiment of the present invention;

[0054] Figure 2 A schematic diagram of the control principle of a fuel cell energy supply system provided by an embodiment of the present invention;

[0055] Figure 3 A schematic diagram of an energy management strategy in a control method for a fuel cell energy supply system provided by the present invention;

[0056] Figure 4 Schematic diagram of an aircraft flight profile in an embodiment of the present invention. DETAILED DESCRIPTION

[0057] In order to make the purpose, technical solution and advantages of the present invention more clear, the embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be noted that the embodiments and features in the embodiments of the present application can be combined with each other arbitrarily without conflict.

[0058] The above background technology has explained several conventional control strategies for energy management control of existing fuel cell energy supply systems; and explained that the existing energy management control methods only consider the minimum equivalent hydrogen consumption of the fuel cell or adjust the power according to the battery charge state, but do not consider the working state of the fuel cell itself, which will cause the fuel cell output power to be not optimal.

[0059] In order to improve the economy and service life of fuel cells, an embodiment of the present invention provides a fuel cell energy supply system and a control method thereof, specifically an energy management control scheme that combines the fuel cell's own state, the battery charge state, and the load demand power.

[0060] The present invention provides the following specific embodiments which can be combined with each other. The same or similar concepts or processes may not be described in detail in some embodiments.

[0061] Figure 1 A schematic diagram of the system structure of a fuel cell energy supply system provided by an embodiment of the present invention. Figure 1 As shown, the main structure of the fuel cell energy supply system provided by the embodiment of the present invention includes: an energy management device, a fuel cell, a battery, a unidirectional DCDC converter, a bidirectional DCDC converter, a bus bar respectively connected to the energy management device, and various onboard loads connected to the bus bar.

[0062] like Figure 1 In the fuel cell energy supply system structure shown, the fuel cell is used as the main power source, connected to the bus bar through a unidirectional DCDC converter to provide basic power for each load, and the unidirectional DCDC converter performs voltage stabilization and power conversion. In addition, the battery is used as an auxiliary power source, for example Figure 1 The lithium battery in the system is connected to the bus bar through a bidirectional DCDC to provide power compensation for each load.

[0063] The energy management device in the embodiment of the present invention is used to collect the aircraft's required power in real time through the bus (including load power, collected through the voltage on the bus), and to allocate the optimal output power to the fuel cells and batteries in the fuel cell power supply system through the real-time collected fuel cell status and battery charge status.

[0064] In an implementation manner of the embodiment of the present invention, two PI control algorithm modules are configured in the energy management device, and the two PI control algorithm modules correspondingly control the unidirectional DCDC converter and the bidirectional DCDC converter.

[0065] In one implementation of the embodiment of the present invention, Figure 2As shown, it is a schematic diagram of the control principle of the fuel cell energy supply system provided by an embodiment of the present invention. In this implementation, on the one hand, the input of the PI control algorithm module corresponding to the bidirectional DCDC converter is the voltage collected through the bus bar and the real-time current of the battery, and the output of the bidirectional DCDC converter is controlled according to the allocated power to achieve the output voltage stability and automatic adjustment of the output current of the bidirectional DCDC converter.

[0066] On the other hand, the input of the PI control algorithm module corresponding to the unidirectional DCDC converter is the voltage collected through the bus bar and the real-time current of the fuel cell. The output of the unidirectional DCDC converter is controlled according to the allocated power to achieve the output voltage stability and automatic adjustment of the output current of the unidirectional DCDC converter.

[0067] Based on the fuel cell energy supply system provided by the embodiment of the present invention, the control method provided by the embodiment of the present invention is a method for controlling the output power of the fuel cell and the battery in the fuel cell energy supply system provided by any of the above embodiments, including the following steps:

[0068] Step 1: During the flight, the aircraft can monitor the bus voltage changes in real time to obtain the aircraft power demand P. req ;

[0069] In this step, according to the flight profile of the aircraft, the aircraft power requirement P of the aircraft in different flight phases can be monitored. req ;like Figure 4 , which is a schematic diagram of an aircraft flight profile in an embodiment of the present invention.

[0070] Step 2: Use the model predictive control algorithm to achieve the optimal control effect at every moment as the control goal, and calculate the optimal power P of the fuel cell at the current moment. bestfc .

[0071] Step 3: Real-time monitoring of the actual battery output voltage V bat 、Current I bat and state of charge SOC;

[0072] In this step, in order to avoid overcharging or overdischarging of the battery, during real-time monitoring, the battery charging and discharging are controlled to ensure that the battery SOC remains within the normal operating range and the SOC target value is determined.

[0073] Among them, the SOC target value is 0.5*(SOC min +SOC max ); SOC min is the lower limit of battery SOC, SOC max It is the upper limit of battery SOC.

[0074] Step 4: Based on the real-time monitored aircraft power demand, the calculated optimal power of the fuel cell at the current moment, and the battery charge state, power is allocated through an energy management strategy to allocate optimal power to the fuel cell power supply system.

[0075] Step 5: According to the optimal power allocated to the fuel cell power supply system, the unidirectional DCDC converter and the bidirectional DCDC converter are controlled to adjust the output power of the fuel cell and the battery respectively.

[0076] In one implementation of the embodiment of the present invention, the above step 2 of calculating the optimal power of the fuel cell at the current moment includes:

[0077] The current state of the fuel cell is monitored, and the model predictive control algorithm is used. The current low calorific value and hydrogen pressure of the fuel cell are used as the model input. Based on the historical data of the fuel cell and the future input predicted by the model, the optimal control effect is achieved at each moment as the control goal, and the optimal power P of the fuel cell at the current moment is obtained. bestfc .

[0078] In a specific implementation of this implementation, the implementation process of the above step 2 may include:

[0079] The objective function of the model predictive control algorithm is set as:

[0080] f=minm H2 (t);

[0081] According to the change of hydrogen pressure, the hydrogen consumption rate can be obtained as:

[0082]

[0083] Among them, p is the hydrogen pressure, n is the number of cells in the stack, M is the molar mass of hydrogen, V is the water volume of the hydrogen storage bottle and the volume of the pipeline, R is the gas constant of the hydrogen storage tank, T is the tank temperature, and Z is the hydrogen compression factor under the conditions of p and T. It can be seen from the hydrogen consumption rate formula that the hydrogen consumption rate of the fuel cell can be adjusted by controlling the hydrogen pressure.

[0084] The optimal output power of the fuel cell at the current moment is obtained by using the low calorific value of hydrogen and the hydrogen consumption rate in actual measurement:

[0085] P bestfc =η fc L HV m H2 ;

[0086] Among them, L HV is the lower calorific value of hydrogen; η FC The efficiency of the fuel cell.

[0087] In addition, the power constraint for the fuel cell is:

[0088] P fc_min ≤P fc (k)≤P fc_max ;

[0089] Among them, P fc_min is the minimum output power of the fuel cell, P fc_max is the maximum power that the fuel cell can output, P fc is the fuel cell power at the current moment.

[0090] In one implementation of the embodiment of the present invention, the energy management strategy in step 4 above includes two strategies, such as Figure 3 FIG. 1 is a schematic diagram of the energy management strategy in the control method of the fuel cell energy supply system provided by the present invention. The specific description is as follows:

[0091] Strategy 1: When the fuel cell output power is insufficient to bear the aircraft's required power, that is, P fc <P req When the battery is discharged to the lower limit of the charge state, the discharge stops and the aircraft requires power P req Provided by fuel cells.

[0092] The above strategy 1 specifically includes:

[0093] When the optimal power of the fuel cell at the current moment and the maximum discharge power of the battery cannot meet the aircraft's required power at the current moment, that is, P req -P bestfc >P dischgmax When the power distribution of the fuel cell and the battery is: the fuel cell and the battery both output at the maximum power, that is, P fc =P fcmax , P bat =P dischgmax ;

[0094] When the fuel cell has the optimal output power P at the current moment bestfc The maximum discharge power of the battery can meet the aircraft's current power demand, that is, P req -P bestfc ≤P dischgmax When the power distribution of the fuel cell and the battery is: the fuel cell outputs the optimal power at the current moment, and the battery bears the remaining power required by the aircraft, that is, P fc =P bestfc , P bat =P req -P bestfc ;

[0095] Among them, the maximum discharge power of the battery is:

[0096]

[0097] Among them, v oc is the open circuit voltage of the battery, r dis is the internal resistance of the battery discharge, and vo is the starting voltage of the battery.

[0098] Strategy 2: When the fuel cell output power can meet the aircraft's required power, that is, P fc ≥P req When the SOC of the battery is reached, the fuel cell stops charging the battery through the bus.

[0099] This strategy 2 includes:

[0100] If the battery SOC is greater than the target value, the battery does not need to be charged. The fuel cell only needs to supply power to the onboard load, and its output power is the load demand power, that is, P fc =P req .

[0101] If the battery SOC is less than the target value, case 1, when the optimal output power of the fuel cell at the current moment is greater than or equal to the sum of the aircraft's required power and the battery's maximum charging power, that is, P bestfc ≥P req +P chgmax , the power distribution of fuel cell and battery is: the output power of fuel cell is the sum of the aircraft power requirement and the battery power requirement, and the battery charging power is its maximum charging power, that is, P fc =P req +P bat , P bat =P chgmax ; Case 2: When the optimal output power of the fuel cell at the current moment is less than the sum of the aircraft's required power and the battery's maximum charging power, that is, P bestfc <P req +P chgmax When the fuel cell and battery power are distributed, the fuel cell output power is the optimal output power at the current moment, and the battery charging power is the remaining power after the fuel cell supplies power to the onboard load, that is, P fc =P bestfc , P bat =P bestfc -P req .

[0102] Among them, the maximum charging power of the battery is:

[0103]

[0104] Among them, r chg is the internal resistance of battery charging, v batmax The maximum allowable battery voltage.

[0105] The fuel cell energy supply system and control method thereof provided in an embodiment of the present invention include: an energy management device, a fuel cell, a battery, a unidirectional DCDC converter, a bidirectional DCDC converter, a bus bar connected to the energy management device, and various loads on board connected to the bus bar; wherein the fuel cell is used as the main power source, connected to the bus bar through a unidirectional DCDC converter, and provides basic power for the electrical equipment, and the unidirectional DCDC converter performs voltage stabilization and power conversion; the battery is used as an auxiliary power source and because it needs to be charged and discharged, the battery is connected to the bus bar through a bidirectional DCDC converter to perform power compensation for the electrical equipment. The fuel cell energy supply system must not only meet the bus voltage stability on the bus bar, but also meet the power demand when the load changes. Under different flight conditions, the energy management device controls the fuel cell and the battery to jointly power the electrical equipment on board.

[0106] In order to adjust the output power of the fuel cell and the battery as quickly as possible, the technical solution provided by the embodiment of the present invention adopts a PI control algorithm to control the DCDC converter in the energy management device. On the one hand, the bidirectional DCDC converter at the rear end of the battery adopts a double closed-loop control (the voltage loop is the outer loop and the current loop is the inner loop), and its corresponding PI control algorithm module controls the output of the bidirectional DCDC converter according to the voltage collected through the bus bar and the real-time current of the battery, so as to achieve the output voltage stability and automatic adjustment of the output current of the bidirectional DCDC converter; in addition, the steady-state characteristics and transient characteristics of the bidirectional DCDC can be improved through current feedback. On the other hand, the unidirectional DCDC at the rear end of the fuel cell also adopts a single closed-loop control, and the control loop is the fuel cell current loop. The unidirectional DCDC is controlled by the fuel cell power allocated by the energy management device and the actual output current of the fuel cell, so as to adjust the output power of the fuel cell. Since the output characteristics of the fuel cell are soft, the "oxygen starvation" phenomenon will occur when the load demand suddenly changes, and the bus voltage is in a stable state, so the fuel cell can be protected by controlling the output current value and current change rate of the fuel cell.

[0107] The implementation effects of the fuel cell energy supply system and the control method thereof provided by the embodiment of the present invention are described below through an implementation example.

[0108] Implementation Example

[0109] This implementation example provides a fuel cell energy supply system and a control method thereof. The system structure and control principle of the fuel cell energy supply system provided by this implementation example are as follows: Figure 1 and Figure 2 shown.

[0110] In this implementation example, the peak power demand of a certain multi-electric aircraft is set to 60kW. The power supply system of the multi-electric aircraft is 270VDC, so the DC bus voltage of the fuel cell power supply system is 270V. The system structure of the fuel cell power supply system in the multi-electric aircraft is as follows: Figure 1 As shown. During the takeoff and climb phase of the aircraft, the fuel cell output characteristics are soft and the start-up is slow, so the battery is needed to assist the fuel cell to power the load. When the aircraft power demand exceeds the power that the fuel cell can provide, the battery is also needed as an auxiliary power source to power the load.

[0111] In the fuel cell energy supply system, the rated output power of the fuel cell is 60kW, the rated voltage is 200-400V, the single-phase DCDC converter adopts a BUCK topology; the output voltage of the battery is 200V, and the rated capacity is 60Ah.

[0112] The energy management device is connected to the bus bar, fuel cell and battery respectively, and can collect the aircraft's required power, fuel cell status and battery state of charge SOC in real time, and allocate the optimal output power to the fuel cell and battery in the power supply system. The implementation steps of the method for controlling the output power of the fuel cell and battery in the fuel cell power supply system using the fuel cell power supply system are as follows:

[0113] Step 1: During the flight, the aircraft can monitor the bus voltage changes in real time to obtain the aircraft power demand P. req .

[0114] Step 2: Monitor the current state of the fuel cell, and obtain the optimal power P that the fuel cell can output based on the current state of the fuel cell. bestfc .

[0115] Step 3: Real-time monitoring of the actual battery output voltage V bat 、Current I bat and state of charge SOC;

[0116] In this step, in order to avoid overcharging or over-discharging of the battery, the battery SOC upper limit is set to 0.95 and the lower limit is set to 0.15 during real-time monitoring. It is necessary to ensure that the SOC can be maintained within the normal working range [0.15, 0.95]. At this time, the SOC target value is 0.6.

[0117] Step 4: Based on the real-time monitored aircraft power demand, the calculated optimal power of the fuel cell at the current moment, and the battery charge state, Figure 3The energy management strategy shown is used to allocate power to allocate optimal power to the fuel cell power supply system. The energy management strategy in this implementation example is specifically:

[0118] Strategy 1: When the fuel cell output power is insufficient to bear the aircraft's required power, that is, P fc <P req When the battery is discharged to the lower limit of the charge state of 0.15, the discharge stops and the aircraft requires power P req Provided by fuel cells.

[0119] When the optimal power of the fuel cell at the current moment and the maximum discharge power of the battery cannot meet the aircraft's required power at the current moment, that is, P req -P bestfc >P dischgmax When the power distribution of the fuel cell and the battery is: the fuel cell and the battery both output at the maximum power, that is, P fc =P fcmax , P bat =P dischgmax ;

[0120] When the fuel cell has the optimal output power P at the current moment bestfc The maximum discharge power of the battery can meet the aircraft's current power demand, that is, P req -P bestfc ≤P dischgmax When the power distribution of the fuel cell and the battery is: the fuel cell outputs the optimal power at the current moment, and the battery bears the remaining power required by the aircraft, that is, P fc =P bestfc , P bat =P req -P bestfc ;

[0121] Strategy 2: When the fuel cell output power can meet the aircraft's required power, that is, P fc ≥P req When the SOC of the battery reaches the upper limit of 0.95, the fuel cell stops charging the battery through the bus.

[0122] If the battery SOC is greater than the target value of 0.6, the battery does not need to be charged; the fuel cell only supplies power to the onboard load, and its output power is the load demand power, that is, P fc =P req ;

[0123] If the battery SOC is less than the target value of 0.6, there are two cases: Case 1, when the optimal output power of the fuel cell at the current moment is greater than or equal to the sum of the aircraft's required power and the battery's maximum charging power, that is, P bestfc ≥P req +P chgmax , the power distribution of fuel cell and battery is: the output power of fuel cell is the sum of the aircraft power requirement and the battery power requirement, and the battery charging power is its maximum charging power, that is, P fc =P req +P bat , P bat =P chgmax ; Case 2: When the optimal output power of the fuel cell at the current moment is less than the sum of the aircraft's required power and the battery's maximum charging power, that is, P bestfc <P req +P chgmax When the fuel cell and battery power are distributed, the fuel cell output power is the optimal output power at the current moment, and the battery charging power is the remaining power after the fuel cell supplies power to the onboard load, that is, P fc =P bestfc , P bat =P bestfc -P req .

[0124] Step 5: According to the optimal power allocated to the fuel cell power supply system, the unidirectional DCDC converter and the bidirectional DCDC converter are controlled to adjust the output power of the fuel cell and the battery respectively.

[0125] In the embodiment of the present invention, in order to quickly and reasonably adjust the output power of the fuel cell and the battery, the following is adopted: Figure 3 The control strategy of the fuel cell power generation system shown in the figure. The bidirectional DCDC converter at the rear end of the battery adopts dual closed-loop control (the voltage loop is the outer loop and the current loop is the inner loop). The corresponding PI control algorithm module controls the output of the bidirectional DCDC converter based on the voltage collected through the bus bar and the real-time current of the battery, so as to achieve the output voltage stability and automatic adjustment of the output current of the bidirectional DCDC converter; the steady-state characteristics and transient characteristics of the bidirectional DCDC converter can be improved through current feedback. The unidirectional DCDC converter at the rear end of the fuel cell adopts a single closed-loop control. The control loop is the fuel cell current loop. The unidirectional DCDC converter is controlled by the fuel cell power allocated by the energy management device and the actual output current of the fuel cell, thereby adjusting the output power of the fuel cell.

[0126] Although the embodiments disclosed in the present invention are as above, the contents are only embodiments adopted to facilitate understanding of the present invention and are not intended to limit the present invention. Any technician in the field to which the present invention belongs can make any modifications and changes in the form and details of implementation without departing from the spirit and scope disclosed in the present invention, but the patent protection scope of the present invention shall still be subject to the scope defined in the attached claims.

Claims

1. A fuel cell energy supply system, characterized in that: include: An energy management device, a fuel cell, a battery, a unidirectional DCDC converter, a bidirectional DCDC converter, a bus bar respectively connected to the energy management device, and various onboard loads connected to the bus bar; The fuel cell is used as the main power source and is connected to the bus bar through a unidirectional DCDC converter to provide basic power for each load, and the unidirectional DCDC converter performs voltage stabilization and power conversion; The battery is used as an auxiliary power source and is connected to the busbar via a bidirectional DCDC to provide power compensation for each load; The energy management device is used to collect the aircraft power demand in real time through the bus bar, and allocate the optimal output power to the fuel cell and battery in the fuel cell power supply system through the real-time collected fuel cell state and battery charge state.

2. The fuel cell energy supply system according to claim 1, characterized in that: The energy management device is configured with two PI control algorithm modules, and the two PI control algorithm modules correspondingly control the unidirectional DCDC converter and the bidirectional DCDC converter.

3. The fuel cell energy supply system according to claim 2, characterized in that: The input of the PI control algorithm module corresponding to the bidirectional DCDC converter is the voltage collected through the bus bar and the real-time current of the battery. The output of the bidirectional DCDC converter is controlled according to the allocated power to achieve the output voltage stability and automatic adjustment of the output current of the bidirectional DCDC converter; The input of the PI control algorithm module corresponding to the unidirectional DCDC converter is the voltage collected through the bus bar and the real-time current of the fuel cell. The output of the unidirectional DCDC converter is controlled according to the allocated power to achieve the output voltage stability and automatic adjustment of the output current of the unidirectional DCDC converter.

4. A control method for a fuel cell energy supply system, characterized in that: The control method is a method for controlling the output power of a fuel cell and a battery in a fuel cell energy supply system according to any one of claims 1 to 3, comprising: Step 1: During the flight, the aircraft can monitor the bus voltage changes in real time to obtain the aircraft power demand P. req ; Step 2: Use the model predictive control algorithm to achieve the optimal control effect at every moment as the control goal, and calculate the optimal power P of the fuel cell at the current moment. bestfc ; Step 3: Real-time monitoring of the actual battery output voltage V bat 、Current I bat And the state of charge SOC; during the real-time monitoring process, the battery charge and discharge are controlled to ensure that the battery SOC remains within the normal working range; Step 4: Based on the real-time monitored aircraft power demand, the calculated optimal power of the fuel cell at the current moment, and the battery charge state, power is allocated through an energy management strategy to allocate optimal power to the fuel cell power supply system; Step 5: According to the optimal power allocated to the fuel cell power supply system, the unidirectional DCDC converter and the bidirectional DCDC converter are controlled to adjust the output power of the fuel cell and the battery respectively.

5. The control method of the fuel cell energy supply system according to claim 4, characterized in that: The step 2 of calculating the optimal power of the fuel cell at the current moment includes: The current state of the fuel cell is monitored, and the model predictive control algorithm is used. The current low calorific value and hydrogen pressure of the fuel cell are used as the model input. Based on the historical data of the fuel cell and the future input predicted by the model, the optimal control effect is achieved at each moment as the control goal, and the optimal power P of the fuel cell at the current moment is obtained. bestfc .

6. The control method of the fuel cell energy supply system according to claim 5, characterized in that: The step 2 of calculating the optimal power of the fuel cell at the current moment includes: Step 21, set the objective function of the model predictive control algorithm to: f = minm H2 (t); Step 22, according to the change of hydrogen pressure, the hydrogen consumption rate is obtained as follows: Wherein, p is the hydrogen pressure, n is the number of cells in the stack, M is the molar mass of hydrogen, V is the water volume of the hydrogen storage bottle and the volume of the pipeline, R is the gas constant of the hydrogen storage tank, T is the tank temperature, and Z is the hydrogen compression factor under the conditions of p and T; Step 23, using the lower calorific value of hydrogen and the hydrogen consumption rate in actual measurement to obtain the optimal output power of the fuel cell at the current moment: P bestfc =η fc L HV m H2 ; Among them, L HV is the lower calorific value of hydrogen; η FC for the efficiency of the fuel cell; Based on the power constraints of the fuel cell, the optimal power P of the fuel cell at the current moment is calculated. bestfc The power constraint of the fuel cell is as follows: P fc_min ≤P fc (k)≤P fc_max ; Among them, P fc_min is the minimum output power of the fuel cell, P fc_max is the maximum power that the fuel cell can output, P fc is the fuel cell power at the current moment.

7. The control method of the fuel cell energy supply system according to claim 4, characterized in that: The energy management strategy in step 4 includes: Strategy 1: When the fuel cell output power is insufficient to bear the aircraft's required power, that is, P fc <P req When the battery is discharged to the lower limit of the charge state, the discharge stops and the aircraft requires power P req Provided by fuel cells; Strategy 2: When the fuel cell output power can meet the aircraft's required power, that is, P fc ≥P req When the SOC of the battery is reached, the fuel cell stops charging the battery through the bus.

8. The control method of the fuel cell energy supply system according to claim 7, characterized in that: The strategy 1 includes: When the optimal power of the fuel cell at the current moment and the maximum discharge power of the battery cannot meet the aircraft's required power at the current moment, that is, P req -P bestfc >P dischgmax When the power distribution of the fuel cell and the battery is: the fuel cell and the battery both output at the maximum power, that is, P fc =P fcmax , P bat =P dischgmax ; When the fuel cell has the optimal output power P at the current moment bestfc The maximum discharge power of the battery can meet the aircraft's current power demand, that is, P req -P bestfc ≤P dischgmax When the power distribution of the fuel cell and the battery is: the fuel cell outputs the optimal power at the current moment, and the battery bears the remaining power required by the aircraft, that is, P fc =P bestfc , P bat =P req -P bestfc ; Among them, the maximum discharge power of the battery is: Among them, v oc is the open circuit voltage of the battery, r dis is the internal resistance of the battery discharge, v o is the starting voltage of the battery.

9. The control method of the fuel cell energy supply system according to claim 7, characterized in that: Strategy 2 includes: If the battery SOC is greater than the target value, the battery does not need to be charged; the fuel cell only supplies power to the onboard load, and its output power is the load demand power, that is, P fc =P req ; If the battery SOC is less than the target value, there are two cases: Case 1, when the optimal output power of the fuel cell at the current moment is greater than or equal to the sum of the aircraft's required power and the battery's maximum charging power, that is, P bestfc ≥P req +P chgmax , the power distribution of fuel cell and battery is: the output power of fuel cell is the sum of the aircraft power requirement and the battery power requirement, and the battery charging power is its maximum charging power, that is, P fc =P req +P bat , P bat =P chgmax ; Case 2: When the optimal output power of the fuel cell at the current moment is less than the sum of the aircraft's required power and the battery's maximum charging power, that is, P bestfc <P req +P chgmax When the fuel cell and battery power are distributed, the fuel cell output power is the optimal output power at the current moment, and the battery charging power is the remaining power after the fuel cell supplies power to the onboard load, that is, P fc =P bestfc , P bat =P bestfc -P req ; Among them, the maximum charging power of the battery is: Among them, r chg is the internal resistance of battery charging, v batmax The maximum allowable voltage of the battery.

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